While a number of structures of various flavodoxins are known, no high resolution solution structures have been published and a number of questions remain regarding the variability of the redox potential of the flavin moeity of different flavodoxins. The anabaena flavodoxin has been studied extensively in this laboratory, but to this point neither the complete 1H, 13C, and 15N resonance assignments nor the complete three-dimensional structure have been determined. Recently, a 13C, and 15N labeled sample of flavodoxin was made, and a number of 3D triple-resonance experiments have been acquired. Additional data required for the stereospecific assignment of all sidechain protons will be collected, as well as 3D and 4D NOESY data. It is anticipated that the high degree of chemical shift dispersion of flavodoxin will allow a very large number of NOE-derived distance constraints to be identified, and that a highly refined structure will be produced using standard distance-geometry and simulated annealing methods.